1. Field of the Invention
The invention relates to a technical field of light emitting diodes (LEDs), in particular to a self-adaptive drive circuit and an LED lamp with the same.
2. Description of the Prior Art
LED, having high luminous efficiency, long service life, solid light source, without polluting heavy metal elements, and other remarkable advantages, is now becoming a new generation of light source and leading a third illumination revolution after the incandescent lamps and the fluorescent lamps.
LED (light emitting diode) has electrical features similar to those of a diode, which is a constant voltage device and is very sensitive to an applied working voltage, and the I/V thereof is in a relation of exponential rise. Generally, the LED can work normally by incorporating a drive power supply that can provide a current-limiting function or a constant current function, and the input mains supply is converted to the constant DC (direct current) generally by adopting a special LED power supply to drive the LED to work stably.
The LED drive power supply generally adopts an AC to DC circuit such as a flyback, or a logical link control (LLC), which may contain an input filter, a rectifier, a constant current and control circuit, a metal oxide semiconductor (MOS) transistor, a transformer, an output rectifier filter and the like. Accordingly, the elements are numerous, the circuit is complex, the design is difficult, and the cost is therefore high. For example, the cost of high quality LED drive power supply is about 1.5-3 yuan/W. Since the circuit usually contains various elements, especially those with life limitation, such as electrolytic capacitor, the life of the drive power supply is limited, thereby limiting the life of the whole LED lamp as well. In most cases, the power supply malfunctions before the LED lamp beads reach the service lives, so the advantage of long life of the LED cannot be fully exerted. Moreover, since the circuit works in a high-frequency switch state, and electromagnetic interference is inevitably generated, which is easy to affect the power grid and bring to bad effects to surrounding radio equipment. Accordingly, the electro magnetic compatibility (EMC) design of the drive power supply is still a big problem that puzzles the designing engineers.
Recently, an alternating-current LED lamp without using a drive power supply appears in the market, wherein the alternating-current LED lamp beads (or reversed common lamp beads) are directly connected to the mains supply by the resistors that limit the currents. It is advantageous that the drive power supply is not used, the cost is low and the life is not limited by the power supply. However, since many LED lamp beads are connected in series and connected to the mains supply, the total voltage of the LED lamp beads approaches the effective value of the mains supply, leading to a fatal defect including the serious stroboflash phenomenon, and since the power factor is low, the harmonic may cause large disturbance to the power grid.
A patent “LED Working Mode Control Device (Chinese patent publication number 202503745U”) also provides an LED driving mode which connects the LEDs to the power supply section by section to adapt to power supply voltage fluctuation (for example, after the mains supply is rectified). By utilizing a switchable short-circuit LED module, when the power supply voltage is low, fewer LEDs are connected; when the power supply voltage is high, more LEDs are connected, thereby making the LEDs being able to adapt to the power supply voltage fluctuation. However, the controllable switches in the disclosure are all connected in series to the LED circuits. Since the controllable switch may itself contain the saturation voltage drop or the turn-on resistance, it is bound to consume more powers. When the lower the input voltage is, the more the series controllable switches are, leading to higher resistance of the controllable switches and more consumed power. The efficiency of the circuit is therefore greatly reduced. Meanwhile, the voltage detection and switch control part provided by the patent is independent, so many elements are adopted, and the circuit is complex.